Tree-felling heads are well known devices installed at the end of a power operated boom carried by a forest-going vehicle. Felling heads are usually provided with a circular saw rotating in a generally horizontal plane for cutting the trees. Arms are provided for grabbing the tree being cut, and subsequently laying it on the ground. Multiple arms may be provided for accumulating a number of trees before putting them down. An example of such a felling head is shown in Canadian patent No. 2,038,784 (GILBERT).
Efforts are being made in the wood cutting industry to increase the cutting capacity of tree-felling heads. Such an increase is particularly significant in regions, such as Western Canada, where trees are wide, of irregular shape, heavy and measure over 100 feet. Standard tree-felling head having a cutting capacity of 24″ often need to cut such trees in repetitive steps which increases operational hazards.
Obtaining a greater cutting capacity may be achieved by either increasing the saw diameter, or reducing the size of the surrounding cage ensuring its proper working. The latter option being difficult to contemplate without affecting the reliability of the system, increasing the diameter remains the better option. However, one important consequence of this expansion is the corresponding increase in the gyroscopic forces acting on the saw. For example, when the felling head is angled forward to put down the cut trees, the saw experiences a sideways tilting which puts heavy constraints on the saw's driving systems and interferes with its ability to resume the desired rotation speed quickly.
There is therefore a need for a mechanism allowing an increase of the diameter of the saw of a tree-felling head without unduly burdening its driving system.